Infection with Pseudomonas aeruginosa (PA) continues to be a major cause of morbidity and mortality in immunocompromised patients, children with cystic fibrosis and in burn patients. Prevention of infection with PA in these patients would seem crucial in reducing such morbidity and mortality since therapy with appropriate antibiotics is often ineffective. Current vaccines to PA, however, have been disappointing due to a toxicity and/or poor immunogenicity in immunocompromised individuals and young children. An alternative to these vaccines are anti-idiotypic antibodies. These antibodies, directed against other antibodies, may resemble an internal image of antigen and are capable of eliciting an antigen-specific antibody response. Recent studies have suggested that anti-idiotypes can prevent experimental infections with bacteria and viruses, are immunogenic in very young animals with immature, poorly functioning immune systems, and are important in the regulation of the overall antibody response to many antigens. This project is designed to produce and test in animal models an anti-idiotypic vaccine against P. aeruginosa. The first step in the study involves production of murine monoclonal idiotypes that are directed against the high molecular weight polysaccharide antigen of PA, which is a nontoxic derivative of LPS. These antibodies will be functionally characterized and the characteristics most likely to produce anti-idiotypes determined. The antibodies will then be used as immunogens in mice to make anti-idiotypic monoclonal antibodies. We will then use these anti- idiotypes in specific animal models to determine: 1) If anti- idiotypic antibodies are immunogenic in animals and if the immune response made to these antibodies resembles that made if antigen alone was used, 2) If immunization with anti-idiotypes prevents infection and/or colonization with PA, and 3) If anti-idiotypes can be utilized to regulate the immune response to PA, 4) What characteristics of the anti-idiotypes are important for antigen specific immune response and immunoregulation (i.e. affinity, isotype), 5) If the murine PA anti-idiotypes can work across species barriers. These studies will provide a model for the production of other anti-idiotypic bacterial vaccines and will increase our understanding of the regulation of the mammalian host response to PA infections. In addition, the proposal will lay the groundwork for preliminary human studies to utilize anti-idiotypes as immunogens or immunoregulators in patients subject to PA infections.